Ink jet recording is a process in which an ink composition are ejected as droplets through minute nozzles to record letters or images (hereinafter also simply referred to as images) on surfaces of recording media. Ink jet recording systems put into practical use include a process in which an electric signal is converted to a mechanical signal by the use of an electrostrictive element to intermittently ejecting an ink composition stored in a nozzle head section, thereby recording letters or images on a surface of a recording medium; and a process in which an ink composition stored in a nozzle head section is rapidly heated at a portion very close to an ejection portion to generate bubbles, and the ink composition is intermittently ejected by volume expansion due to the bubbles to record letters or images on a surface of a recording medium.
Further, the ink composition for ink jet recording is generally a solution of various dyes in water, an organic solvent or a mixture thereof, and requires severer requirements than an ink composition for writing materials such as a fountain pen and a ball point pen in terms of stability and printing characteristics.
In view of the fact that ink jet printers have recently been employed for the preparation of printed matter for advertisement, even severer requirements have come to be required in forming a color image using a plurality of ink compositions.
The reason for this is that when even one color inferior in hue exists in the color image formed by the plurality of ink compositions, the hue causes poor color balance as the whole image, resulting in the difficulty of obtaining a high-quality image.
In particular, “photographic image quality” printing with color ink jet printers has reached a level not inferior to that of “silver salt photographs” and has also become “equivalent to photographs” in image quality by successive improvements of heads, ink compositions, recording processes and media, respectively. On the other hand, keeping quality of images obtained has also been improved by improvements of ink compositions and media. In particular, light resistance has been improved to a level having practically no problem. However, it does not reach a level comparable to the silver salt photographs. As for evaluation of the ability of light resistance, judgments have normally been made using the color fading rate of a pure color pattern (the optical density is about 1.0) of each of Y, M and C as an index. With respect to the ability of heat resistance of ink compositions carried by printers commercially available on the market at present, the ability of magenta ink compositions is lowest when judged using the above-mentioned evaluation technique. Accordingly, it leads to improvement in the light resistance of images equivalent to photographs to improve the light resistance of the magenta compositions.
From such a viewpoint, the present inventors have provided ink sets containing magenta ink compositions improved in the light resistance of images equivalent to photographs by using compounds having specific structures as colorants for the magenta ink compositions (Japanese Patent Application Nos. 2002-120069 and 2002-120070).
In subsequent studies, the present inventors have added a carboxyl group-containing aromatic compound or a salt thereof to the above-mentioned compounds having the specific structures. As a result, the present inventors have known that moisture resistance of the images is also improved.